docs: update Angular integration examples for modern APIs

[ArturQuirino]

Summary

Updates the Angular integration docs so examples follow current Angular patterns: signal-based viewChild / input() and teardown with inject(DestroyRef) instead of @ViewChild, @Input(), and ngOnDestroy.

What changed

• Basic setup — viewChild.required, AfterViewInit, and inject(DestroyRef).onDestroy() for superdoc.destroy(); SuperDoc is created in ngAfterViewInit so the template ref exists.
• Full component — input.required() / input() for inputs; same viewChild + DestroyRef pattern; document and user read via this.document() / this.user().
• Handle file uploads — Restores full imports at the top of the snippet; same viewChild + DestroyRef cleanup; selector uses this.editorRef().nativeElement.

Why

Keeps the Getting Started Angular page aligned with modern Angular and copy-pasteable for recent projects.

Test plan

• pnpm run check:imports
• pnpm run dev:docs — verify Angular Integration page renders and snippets look correct

[caio-pizzol]

@ArturQuirino nice cleanup — the code is correct and consistent across all three snippets, and snippet 3 quietly fixes a missing-imports bug from the old version.

one ask: these examples need Angular 17.1+ (signal-based viewChild() and input() shipped in 17.1). the old examples worked on much older versions. anyone on older Angular who copy-pastes will get errors they won't understand. worth adding a one-liner under the intro on line 7? something like:

Examples use signal-based APIs (viewChild(), input()) introduced in Angular 17.1. For older Angular versions, swap to the decorator-based equivalents (@ViewChild, @Input).

also left a small nit inline on typing the element ref.

[caio-pizzol]

small nit (applies to all three snippets): typing ElementRef<HTMLDivElement> gives nativeElement a real type instead of any. since the template is a <div>, it's a free win.

Suggested change

	private readonly editorRef = viewChild.required<ElementRef>('editor');
	private readonly editorRef = viewChild.required<ElementRef<HTMLDivElement>>('editor');

[ArturQuirino]

Added it as suggested.

[ArturQuirino]

@caio-pizzol I added the text below so it makes it clearer for those using older versions of Angular what they need to change in the code to be able to use the code in this doc.

Examples use signal-based APIs (viewChild(), input()) introduced in Angular 17.1. For older Angular versions, swap to the decorator-based equivalents (@ViewChild, @input).